Formation of Carbon Nanofibers and Carbon Nanotubes through Methane Decomposition over Supported Cobalt Catalysts

Abstract

Catalytic performance of Co catalysts supported on different supports (MgO, Al2O3, SiO2, and TiO2) for the formation of carbon nanofibers through methane decomposition was investigated. Catalytic activity and the life of supported Co catalysts for methane decomposition at 773 K strongly depended on the type of catalytic supports; i.e., the catalytic performances of Co/Al2O3 and Co/MgO were superior to those of Co/TiO2 and Co/SiO2. All the Co catalysts produced carbon nanofibers with relatively uniform diameters (10−30 nm) through the reaction at 773 K irrespective of the kind of catalytic supports, although an average crystallite size of Co metal was different for these catalysts. These results implied that Co metal particles with diameters from 10 to 30 nm grew carbon nanofibers from methane preferentially, while ones larger than 30 nm were inactive for the reaction. The structures of carbons formed by methane decomposition over Co/Al2O3 depended on the reaction temperatures. Multiwalled carbon nanotubes (MWCNT) were produced mainly in the temperature range of 873−973 K, where the catalytically active Co metal particles were present at the tip or in the hollow of MWCNT. On the other hand, helically coiled carbon nanotubes and bamboolike carbon nanotubes were formed preferentially at 1073 K, where Co metal particles could be rarely observed in the carbons. These results implied that the growth mechanisms of these carbons by Co metal particles were changed according to the reaction temperatures. Co K-edge XANES and EXAFS suggested that Co species on the supported Co catalysts were always present as Co metal during the methane decomposition, irrespective of the kinds of catalytic supports or the reaction temperatures.

Growth of carbon nanotubes and microfibers over stainless steel mesh by cracking of methane

“…At a temperature of 750°C and CH 4 pressure at 101 kPa, over the catalysts of Ni/SiO 2 , CuNi/SiO 2 , Rh-Ni/SiO 2 , Pd-Ni/SiO 2 , Ir-Ni/SiO 2 , Pt-Ni/SiO 2 , Pd/SiO 2 , Pd-Ni/Al 2 O 3 , Pd-Ni/TiO 2 , Pd-Ni/MgO and Pd-Ni/ CF (carbon fiber), it was found that the methane conversions were all below 15% [34]. At 500°C and CH 4 pressure of 101 kPa and catalysts of Co/SiO 2 , Co/TiO 2 , Co/MgO and Co/ Al 2 O 3 , the methane conversions were all below 10% [35]. Using the Ni-Cu/Al 2 O 3 catalyst, at 500°C, 600°C, 700°C and 750°C, the methane (undiluted) conversions were around 10%, 22%, 59%, and 65% respectively [36].…”

Large Scale Synthesis of Carbon Nanofibres on Sodium Chloride Support

“…The basic idea behind using a water soluble support returns to Steigerwalt and Lukehart [17] who employed silicate or carbonate. Metal catalysts, such as Fe [18][19][20][21], Ni [22,23], Cu [24], Co [25,26] and their alloys [27], have been investigated widely. However, until now, the reported catalysts require the lengthy process of reduction and calcination for their preparation [11,13].…”

Methane Decomposition: Production of Hydrogen and Carbon Filaments

“…Takenaka et al have recently investigated the effect of supports on CF formation for Co-based catalysts. 79 The Co/Al 2 O 3 and Co/ MgO catalysts were found to be superior to the Co/SiO 2 and the Co/TiO 2 catalysts for CF formation. Based on catalyst characterization studies the authors claimed that the 10-30 nm range for Co particles was preferred for CF formation.…”

“…77 XANES studies showed that during the methane decomposition reaction the smaller sized Fe particles were transformed into Fe 3 C while the larger particles were converted into carbon atom saturated g-Fe species. The supports had a profound effect in determining the nature of the CF formed in the process; multi-walled CF and chain like carbon fibers were formed on Fe/Al 2 O 3 , while CF composed of spherical carbon units were formed along with chain like carbon fibers on Fe 2 O 3 /SiO 2 catalysts.…”